CVE-2021-21698
📋 TL;DR
The Jenkins Subversion Plugin vulnerability allows attackers with agent access to read arbitrary files on the Jenkins controller file system. This affects Jenkins instances using the Subversion Plugin version 2.15.0 or earlier where agents can be configured or controlled by untrusted users.
💻 Affected Systems
- Jenkins Subversion Plugin
📦 What is this software?
Subversion by Jenkins
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of Jenkins controller through reading sensitive files like credentials, configuration files, or SSH keys, potentially leading to full system takeover.
Likely Case
Unauthorized access to sensitive configuration files, credentials, or source code stored on the Jenkins controller.
If Mitigated
Limited impact if proper access controls restrict agent configuration to trusted users only.
🎯 Exploit Status
Exploitation requires agent access but is straightforward once that access is obtained.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.15.1
Vendor Advisory: https://www.jenkins.io/security/advisory/2021-11-04/#SECURITY-2506
Restart Required: Yes
Instructions:
1. Update Jenkins Subversion Plugin to version 2.15.1 or later via Jenkins Plugin Manager. 2. Restart Jenkins to apply the update.
🔧 Temporary Workarounds
Restrict Agent Configuration
allLimit who can configure Jenkins agents to trusted administrators only.
🧯 If You Can't Patch
- Disable or remove the Subversion Plugin if not required
- Implement strict access controls on agent configuration and monitor for unauthorized changes
🔍 How to Verify
Check if Vulnerable:
Check Jenkins Plugin Manager for Subversion Plugin version. If version is 2.15.0 or earlier, the system is vulnerable.Check Version:
Check via Jenkins web interface: Manage Jenkins > Plugin Manager > Installed pluginsVerify Fix Applied:
Verify Subversion Plugin version is 2.15.1 or later in Jenkins Plugin Manager.📡 Detection & Monitoring
Log Indicators:
- Unusual file access patterns from agents
- Failed attempts to access restricted files
Network Indicators:
- Unusual agent-to-controller file transfer patterns
SIEM Query:
source="jenkins.log" AND ("subversion" OR "svn") AND ("file access" OR "path traversal")